w4 Luteal phase Flashcards
Phases of the luteal phase
Metoestrus and Dieostrus
TIme of ovulation until luteolysis of CL
Luteal phase consists of
Luteinisation
Growth and development of CL
Luteolysis
Luteinisation
Day 1-3
Transformation of follicle cells into luteal cells following ovulation (corpus haemorrhagicum)
Growth and development of CL
Increase size and mass
Increase in progesterone production
From day 5 (diestris
Luteolysis
Towards end of dioestrus
Destruction/lysis of CL
Lowers progesterone
Regress CL beocme corpus Albicans (white body) and scars for several cycles
Stages of CL
Corpus Haemorrhagicum
-Bloody body, formed after ovulation - 1-3days
CL - yellow, starts growing day 3-5, produces P4
Corpus Albicans - white, remnants of CL, scar like, remain on ovary
Luteinisation
Transoformation of theca interna and Granulosa to luteal cells
GOVERNED BY lh
Steps of Luteinisation
Breakdown of basement membrane
Collapse of follicle into may folds
Folds interdigitate and mixing of thecal and granulosal cells
Formation of connective tissue networks
Angiogenesis - vascularisation of the CL
Large luteal cells
COme from granulosa (20-40mirco mill
Produce progesterone
Undergo hypertrophy as CL develops - increase size
COntain oxytocin and relaxin
Small Luteal cells
Thecal cells
Less than 20 micrmill
Produce progesterone
Undergo hyperplasia as CL develops (increase numbers
Functionality of CL
Depends on Size
-Blood progesterone is correlated with size of CL
Degree of vascularisation
- ability of a CL to synthesise and deliver progesterone
Target organs of progesterone
Hypothalamus
-Cause negative feedback (reduced basal GnRH pulse frequency)
-Prevents behavoiral oestrus
Prevents pre ovulatory LH surge
Uterus
-Stimulates endometrial gland secretion (supports development of conceptus)
Reduces myometrial tone
Mammary Gland
Promotes alveolar development in mammay gland
Luteolysis
Loss of progesterone secretion by CL and luteal tissue mass
1-3 days at end of luteal phase
Irreversibe degeneration
Induced by PGF2a secreted by uterine endometrium
Requirements of Luteolysus
Oxytocin receptors on endometrial cells
Presence of critcal level of oxytocin
PGF2a syntheses by endomedrium
Oxytocyn
Released from large luteal cell granules
=increased PGF2a
PGF2a
Secreted from endometrium
Reached ipsilateral ovary through vascular countercurrent mechanism in cow, ewe, sow (passive diffusion from uterine vein into the ovarian artery)
Counter current absent in mares (general circulation)
PGF2a
can be used to artificially lyse the CL to synchronise oestrus and induce parturition
Vascular counter current exchange
2 closely associated blood vessels flowing different ways
Low molecular wt substances can flow from one to another
PGF2a flows from uterine vein to ovarian artery
=no dilution through systemic circulation
Mare PGF2a
systemic circulation
Mechanisms of Luteolysis
Ischemia (reduced blood flow)
- PGF2a causes vasoconstricion of blood vessels supplying CL but its still adequta
- Capilary degeneration within CL is more likely
Cellular Mechanisms initiate apoptosis
-PGF2a binds to plasma membrane receptors on large luteal cells
Results in casade of events- activation og protein kinase c(PK-c) inhibits progesterone synthesis
Immune system
-inhibits progesterone synthesise by luteal cells
